On linux-image-2.6.26-1-686 version 2.6.26-3 this adaptor worked fine
and neither of the following problems occurred.

On linux-image-2.6.26-1-686 version 2.6.26-4 there are serious problems.

First, the usb-serial ports do not work correctly. Whatever character
I send to the tty, it emits the letter 'O' from the serial port.
See the two strace attachments, which are from kernels 2.6.26-3 and
2.6.26-4 respectively. They were generated using minicom talking to a
serial device which just echoes the input and sends the prompt "Ready"
when it receives a carriage return.

Unfortunately I didn't type the same characters in each test, but
if you diff the straces you can see that the tiocmget behaviour is
substantially changed in what it returns, in addition to the incorrect
character being sent.

Secondly, on unplugging the adaptor, a kernel OOPS is caused due to a
null pointer dereference. See dmesg extract also attached.

Following this OOPS, lsusb just hangs and is not interruptible with
control-C, and on attempting to shut down the machine the shutdown process
hangs when closing down Bluetooth (the built-in Bluetooth adaptor also
presents a USB interface). Magic sysrq key still works fortunately !

A different usb-serial device using the ftdi-sio driver still works
without error.

I see the following in the package changelog and wonder if this change
is related to the destabilisation ?

Assigning this as "serious" in relation to Lenny rc policy, due to the
fact that this kernel null pointer dereference seems to break the entire
USB subsystem. Please reassign if this is inappropriate, thanks.

On Mon, Sep 08, 2008 at 08:38:20PM +0100, Nick Leverton wrote:[color=blue]
> Package: linux-image-2.6.26-1-686
> Version: 2.6.26-4
> Severity: serious
> Justification: lenny/rc-policy
>
> I have a USB "Express" twin port serial adaptor, which identifies itself
> as USB ID 9710:7840 MosChip Semiconductor. This uses the mos7840 Moschip
> 7840/7820 USB Serial Driver.
>
> On linux-image-2.6.26-1-686 version 2.6.26-3 this adaptor worked fine
> and neither of the following problems occurred.
>
> On linux-image-2.6.26-1-686 version 2.6.26-4 there are serious problems.
>
> First, the usb-serial ports do not work correctly. Whatever character
> I send to the tty, it emits the letter 'O' from the serial port.
> See the two strace attachments, which are from kernels 2.6.26-3 and
> 2.6.26-4 respectively. They were generated using minicom talking to a
> serial device which just echoes the input and sends the prompt "Ready"
> when it receives a carriage return.
>
> Unfortunately I didn't type the same characters in each test, but
> if you diff the straces you can see that the tiocmget behaviour is
> substantially changed in what it returns, in addition to the incorrect
> character being sent.
>
> Secondly, on unplugging the adaptor, a kernel OOPS is caused due to a
> null pointer dereference. See dmesg extract also attached.
>
> Following this OOPS, lsusb just hangs and is not interruptible with
> control-C, and on attempting to shut down the machine the shutdown process
> hangs when closing down Bluetooth (the built-in Bluetooth adaptor also
> presents a USB interface). Magic sysrq key still works fortunately !
>
> A different usb-serial device using the ftdi-sio driver still works
> without error.
>
> I see the following in the package changelog and wonder if this change
> is related to the destabilisation ?
>
> linux-2.6 (2.6.26-4) unstable; urgency=low
> * Add stable release 2.6.26.3:
> - usb-serial: don't release unregistered minors[/color]

The commit in question is
[url]http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.26.y.git;a=commit;h=bb457a9869e945299445f13bf618975d1562ab83[/url]

Please try to a kernel build with that fix reverted. If it fixes
the problem for you, please pass your debug data to Greg Kroah-Hartman
<gregkh@suse.de>, who's both one of the maintainers of the 2.6.26.x stable
releases and the Linux USB maintainer.

Cheers,
Moritz

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